1. Field of the Invention
The present invention relates to an image forming apparatus having a liquid ejection head provided with a plurality of nozzles.
2. Description of Related Art
An ejection face of an inkjet head during printing is exposed to the air. Thus, when non-ejection duration in which no ink is ejected is elongated, the viscosity of ink around an ejection opening of the nozzle is likely to increase. Increase in the viscosity of the ink may cause decrease in a volume of ink ejected from the nozzle, which degrades print precision.
Thus, such a technique is known where, in a recording head capable of forming three different sizes of dots per one pixel, when non-ejection duration after a start of printing operation before a first dot is formed exceeds a permitted period of time, the first dot formed by each nozzle is changed from a small dot and a medium dot to a medium dot and a large dot, respectively, the three different sizes of dots being large, medium, and small.
Such a change in the size of a dot is carried out by changing the number of times an ink droplet is ejected from a nozzle per one pixel. This compensates a volume of ink to be ejected from a nozzle which contains ink whose viscosity has increased, that is, a nozzle in which the volume of ink to be ejected is likely to decrease. As a result, a dot having a desired size can be formed. Further, increasing a size of a first dot to be ejected from a nozzle increases the number of times an ink droplet is ejected through the nozzle. This provides a flushing effect.